University of Maine researchers have demonstrated that the blue mussel can eat larvae of the parasitic sea louse that has been decimating farmed finfish stocks. The results could be highly useful for Maine’s farmed salmon industry.

The findings were published recently in the journal Aquaculture. If further analysis in the field supports these first findings, mussels could be used as another disease management strategy for weakening the infectious pressure of sea lice in finfish farms, as the pest has become resistant to drugs.

The paper could also be good news for Maine’s development of integrated multi-trophic aquaculture (IMTA), an alternative to the standard mono-culture aquaculture. IMTA lowers the environmental impacts of commercial aquaculture by combining fed species, such as salmon, with extractive species, such as mussels.

“Extractive species are filter-feeding so they’re taking in all the phytoplankton and zooplankton and whatever’s in the water column, but they’re also taking in excess fish food and feces and removing all those organics from the water,” postdoctoral researcher Sally Molloy, a microbiologist in UMaine’s School of Marine Sciences explicated.

“The idea is hopefully IMTA practices reduce the amount of nutrients that are going into the ecosystem because of the fish farm. It’s sort of a greener version of farming,” she said.

The research into this and other IMTA-related work is being funded by USD 1.6 million in grants from organisations including Maine Sea Grant, the Maine Technology Institute, the National Oceanographic and Atmospheric Administration, and the Maine Aquaculture Innovation Center.

The sea louse feeds on the skin and tissue of its host. Most research focuses on the stages when it has already infected its host.

UMaine researchers have concentrated on combating the sea louse in its larval stage.

The researchers gathered sea lice egg strings from an infected commercial salmon farm. The eggs hatched and were reared to the copepodid stage.

Meanwhile, the team got mussels from a local commercial mussel farmer and exposed them to the sea lice copepods for 30 or 60 minutes, after which the contents of the mussels’ stomachs were removed for DNA studies which showed that the mussels had ingested the sea lice copepodids.

The UMaine team later this year will insert a mussel raft into the waters of a salmon farm on the Maine coast to determine if their results hold up on a larger scale. The populations of mussels, salmon and sea lice will be monitored for several years to determine how they affect each other.

Ian Bricknell, professor at UMaine’s School of Marine Sciences, said seaweed could be farmed in a larger area surrounding the mussel rafts to round out the site’s productivity. Seaweed growth is fortified by nitrogen and phosphates found in salmon effluent, Bangor Daily News reports.

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